DE1215125B - Process for the purification of gaseous formaldehyde - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY

GERMAN

PATENT OFFICE

EDITORIAL

Int. α .:

C07c

German class: 12 ο-7/01

Number: 1215 125

File number: V 26238IV b / 12 ο

Filing date: June 25, 1964

Opening day: April 28, 1966

The invention relates to a method for cleaning of gaseous formaldehyde, the formaldehyde gas with one on the wall of one perpendicular standing pipe running film of a washing liquid is brought into contact with the aim of obtaining a highly purified gas that is particularly suitable for the production of high molecular weight Polyformaldehyde is suitable.

The removal of water, methanol, formic acid, methyl formate and the like usually liquid contaminants from formaldehyde gases cause considerable technical difficulties, because these impurities lead to the formation of solid low molecular weight at temperatures below 100 ° C Polymer lead, which often give rise to malfunctions and their elimination a complicated apparatus make necessary. To avoid these disadvantages, a method has become known at which the cleaning at higher temperatures with inert to formaldehyde compounds des Polyethylene glycol is carried out. The cleaning effects to be achieved by this method are however, not very satisfactory.

Other known methods are used to purify formaldehyde gases from solid absorption or adsorbents such as phosphorus pentoxide or silicates. However, there is a significant drop in absorption Amounts of low polymers in the mixture with the absorbent during the adsorption regeneration of the adsorbent is cumbersome and costly. Also comes undesirable side reactions occur in this procedure.

In other known processes, the formaldehyde gas is cooled in the presence of inert solvents or solvent mixtures made, whereby it is achieved that the to low molecular weight polyformaldehyde-bound impurities occur as a suspension. These The procedure is associated with considerable losses of formaldehyde and leaves a continuous one Operation is not closed, as the polymerization begins preferentially on the walls of the vessel, which leads to a or the cleaning equipment needs to be changed. In addition, the formation of the low molecular weight Polymers under the known conditions are very uncontrolled, which alone is enough For this reason, the quality of the purified formaldehyde gas is subject to very large fluctuations is.

Finally, it is known to apply formaldehyde gas to a film of hemiacetal in the same or counter process for purifying gaseous
formaldehyde

Applicant:

VEB Leuna-Werke »Walter Ulbricht«,
Leuna (Kr.Merseburg)

Named as inventor:

Dr. Robert Kaufhold,

Dipl.-Ing. Bernd Haase, Leuna (Kr. Merseburg);

Dipl.-Chem. Rolf Kloss, Merseburg

electricity to wash. A straight, smooth-walled tube is used to carry out the process also formed in a spiral or onion shape and with guide surfaces or ribs or with fillers can be provided. However, experience has shown that a longer operating time is only possible with smooth, vertical pipe can be achieved. For the technical execution of the process are therefore also tube bundles made of smooth tubes in which the walls are completely wetted, has been proposed. But even here there are still great difficulties. That's how it is at work in countercurrent already the even distribution of the hemiacetal on the tubes, in particular problematic because of the polymerization which occurs preferentially at the point of application. Also the temperature control the pipes for the purpose of separating the impurities on the one hand and avoiding settlements in the tubes, on the other hand, it is prepared when using hemiacetals with a high formaldehyde content Trouble. Quite apart from the fact that the relatively low ones to be observed Temperatures the polymerization of the formaldehyde at the insufficiently wetted parts of the pipe is very favored, the formaldehyde absorption in the washing liquid is very large. Through this there are poor yields of purified formaldehyde gas and, moreover, too high Polymer deposits in the washing liquid, which in turn lead to further deterioration contribute to the wetting of the pipe. On the other hand, there is the regeneration of the washing liquids very difficult.

The greatest deficiency of this process, however, is the inadequate separation of the gas in the gas stream condensing impurities that just come through

609 560/492

3 4

the use of long, narrow tubes is satisfactorily the most favorable speed is case by case without

can be done. In this case, however, there are large additional factors to be determined empirically. Will be the same

Loss of formaldehyde through absorption in the degree of contamination and the same throughput

Hemiacetal. the circumferential speed of the gas to be cleaned

It has now been found that the character of the rotor is increased, so a cleaner gas is produced.

th process for purification of gaseous hold.

Formaldehyde-adhering disadvantages are avoided by the combination of the invention

the if you can take the formaldehyde gas with one of the measures in easier and more economical

the wall of a vertical pipe - a pure formaldehyde gas can be produced,

running film of a washing liquid in contact i ° the generation of high molecular weight poly-

brings and the cleaning is suitable according to the invention under formaldehyde. It was to be expected

Makes use of a pipe in which a

heatable rotor is arranged coaxially, the rotor movement of the material transfer a good cleaning effect

occurs during the cleaning process under heating, but it could not be foreseen

to at least 70 ° C in revolutions, and 15 den that the amount of formaldehyde absorbed in the

that the washing liquid with a temperature washing liquids under the conditions according to

between -20 and + 130 ° C on the pipe wall of the invention is very low. The improvement

gives up and thereby the temperature of the rotor and the mass transfer from the gas to the liquid

that of the washing liquid, possibly through to phase, accordingly has a particular effect on the im

Additional cooling of the pipe wall, so 20 impurities contained in formaldehyde on each other.

agrees that the formaldehyde gas to be purified is large in size, which is surprising to the person skilled in the art

allow the pipe to a temperature of at least a difference in absorption properties

80 ° C is cooled. even requires adequate cleaning of the mold

The gas can be used both in constant gas and in aldehyde gas at higher working temperatures

to be carried out in countercurrent with the film of the washing liquid 25. The resulting procedural

be brought into contact. Renal technical advantages are very considerable.

As a washing liquid, especially when arriving _. · ] 1
Turning the hemiacetal process into manufacture. .Example
of formaldehyde gas, higher alcohols and / or. The apparatus used consists of a ver or their hemiacetals suitable, whereby the washing table arranged tube made of austenitic chromium liquid at a temperature between -20 and nickel steel of 2 m length and an inside diameter of + 80 ° C is applied to the pipe wall. knife of 200 mm, In the tube is a coaxial

However, other liquids can also be arranged, such as a six-bladed rotor that has a heated

Has hydrocarbons, chlorinated hydrocarbons, esters bare hollow shaft and its wing tips 3 mm

or ether, find use. It is advantageous that they are removed from the pipe wall. The pipe is open

Use of washing liquids that behave on the outside with one on the lower end of the pipe

provided a moderately large dissolving power for formaldehyde incipient cooling jacket of 1.8 m length,

so that the impurities do not, at the top of the pipe are three on the

Polyformaldehyde bound, in the form of a suspen- catch evenly distributed, tangentially arranged

sion, but occur in solution. 40 nozzles for feeding in the washing liquid

A glycol brach is used as the washing liquid.

Glycol hemiacetal mixture, a gas is used for 60 to 62 kg / hour. Formaldehyde gas, which is 9500 ppm for the production of high-polymer formaldehyde water, 1200 ppm methanol and 1020 ppm ants, is already obtained when acid is present as impurities C at the lower end of the speed with additional cooling of the pipe wall so that the pipe is introduced into the apparatus. At the same time it is coordinated that the pipe was discharged through the tangential connection 200 kg / hour. emerging gas has a temperature of 60 ° C, each with a glycol-glycol hemiacetal mixture with a but at lower temperatures a higher content of 43.5 percent by weight formaldehyde, degree of purity of the gas is achieved. If the formaldehyde gas contains a relatively large amount of water, methanol and 0.18 percent by weight of formic acid, or if hemiacetals are introduced into the pipe as washing liquid and trickled into the pipe as closed, the alcohol component has a relatively film down on its inner wall. If the temperature has a high vapor pressure, then the mixture introduced is more intensive at 20.degree. C. It is necessary to cool the pipe wall. 55 the cooling jacket of the pipe were 2 m ³ / h. water

The purpose of the rotor arranged in the tube is to keep it at a temperature of 12 ° C. The rotor

the film running off the pipe wall was operated at a speed of 1200 min- ¹

right to maintain or to form such a film and by means of a glycol circuit on a medium

and to maintain the gas flow with the film leren kept temperature of 80 ° C. That in that

to bring into intimate contact and in the gas stream 60 pipe cooled formaldehyde gas flowing upwards

condensing and polymerizing fractions by themselves on the glycol-glycol hemiacetal film, wherein

centrifugal acceleration in the liquid film the impurities contained in the formaldehyde gas

to transport. These effects are largely absorbed by the liquid film.

Dimensions achieved when using a rotor that was beer. At the top of the pipe there were 50 bis

the one equipped with two or more vertical blades 65 52 kg / hour. Formaldehyde gas with a temperature

is equipped. from 45 ° C. The contaminants remaining in the gas

The circumferential speed of the rotor was 491 ppm water, 240 ppm metha-

expediently between 8 and 20 m / sec; the nol and 25 ppm formic acid. On the lower pipe

at the end, 210 kg / hour fell. a glycol-glycol hemiacetal mixture with a temperature of 86 to 88 ° C, the 47.5 percent by weight formaldehyde, 0.3 percent by weight water, 0.1 percent by weight Methanol and 0.2 percent by weight formic acid.

After an operating time of over 500 hours, none of the purification of the formaldehyde gas was more disruptive Determine polymer build-up in the apparatus.

Example 2

The apparatus used is constructed analogously to that described in Example 1, with the difference that the length of the pipe is 4 m and that of the cooling jacket is 3.7 m and that a rotor is arranged whose horizontal cross-section corresponds to a triangle with inwardly curved sides.

50 kg / hour Formaldehyde gas, which contained 8100 ppm of water, 2800 ppm of methanol and 620 ppm of formic acid as impurities, were introduced into the apparatus at a temperature of 100 ° C. at the upper end of the tube. At the same time, through the tangential nozzles, 200 l / h. Diesel oil purified by means of hydrogen refining and using molecular sieves was introduced into the pipe and trickled down as a closed film on its inner wall. The temperature of the diesel oil was 100 ° C. 6 m ³ / hour were passed through the cooling jacket of the pipe. Cooling brine passed at a temperature of -10 ° C. The rotor ran at a speed of 2000 min. " ¹ and was kept at an average temperature of 95 ° C. by means of a glycol circuit. At the lower end of the tube, the formaldehyde gas was separated from the diesel oil-polyformaldehyde suspension formed. At this point on the tube 44 kg / h of formaldehyde gas emerged at a temperature of 45 ° C. The impurities remaining in the gas were 236 ppm water, 157 ppm methanol and 29 ppm formic acid 32 ° C. It contained about 10 percent by weight of the formaldehyde gas used as low molecular weight polyformaldehyde to which most of the impurities in the gas used were bound.

After an operating time of about 400 hours, the cleaning of the Formaldehyde gases not disturbing polymer build-up found in the apparatus.

Claims (3)

Patent claims: 1. A method for cleaning gaseous formaldehyde, the formaldehyde gas being brought into contact with a washing liquid running down the wall of a vertical tube, characterized in that the cleaning is carried out using a tube in which a heatable rotor is arranged coaxially is offset to the rotor during the cleaning operation while being heated to at least 70 ° C in revolutions, and in that one gives up the wash liquid with a temperature between -20 and + 13O ⁰ C to the tube wall and thereby the temperature of the rotor and the washing liquid, optionally by additional cooling of the pipe wall, coordinated so that the formaldehyde gas to be purified is cooled in the pipe to a temperature of at least 80 ° C. 2. The method according to claim 1, characterized in that the formaldehyde gas in the Co-current or counter-current is brought into contact with the film of the washing liquid. 3. The method according to claim 1 and 2, characterized in that higher than the washing liquid Alcohols and / or their hemiacetals are used and the washing liquid is applied to the pipe wall at a temperature between -20 and + 80 ° C. Considered publications:
German patent application F 10715 (published on 2.1955); German interpretative document No. 1140 921;
Patent Specification No. 28 014 of the Office for Inventions and Patents in the Soviet Zone of Occupation in Germany; Ullmann's Encyclopedia of Industrial Chemistry, 1, 1951, p. 440.